A high voltage generation apparatus supplies a tube voltage to an X-ray tube included in an X-ray CT apparatus. The high voltage generation apparatus needs to improve a power factor in order to meet harmonic regulations. Examples of a method of improving the power factor of the high voltage generation apparatus include a method using a reactor and a method using power factor improvement circuitry (power factor corrector (PFC)).
The use of a reactor improves the power factor of the high voltage generation apparatus to be approximately 0.8. In this case, a reactor compatible with 50 Hz or 60 Hz is used. The power factor obtained by the use of the reactor, however, is smaller than a power factor obtained by the use of power factor improvement circuitry. Furthermore, the reactor compatible with 50 Hz or 60 Hz is large in dimensions and weight. The dimensions and weight of the high voltage generation apparatus are accordingly increased.
The use of power factor improvement circuitry improves the power factor of the high voltage generation apparatus to be approximately 0.95 to approximately 0.99. This enables apparent power of an alternating current (AC) power source configured to supply power to ar X-ray tube to be reduced to suppress the capacity of the AC power source while suppressing the increase in dimensions and weight of the high voltage generation apparatus. When the irradiation of X-rays is started, however, a load applied to the high voltage generation apparatus abruptly increases, and an output voltage of the power factor improvement circuitry decreases. When the irradiation of X-rays is ended, the load applied to the high voltage generation apparatus abruptly decreases, and the output voltage of the power factor improvement circuitry increases. Thus, for example, a tube voltage may fluctuate so that the dose of the X-rays radiated from the X-ray tube may fluctuate.